The Assumption of the Virgin Mary is the belief that Jesus Christ‘s mother Mary was raised into heaven in both body and soul at the moment of her death. There’s some ambiguity as to whether she was raised just before or just after she died.
The idea arose in 4th century apocryphal writings, was accepted by orthodox believers in the 7th century and was formally made Catholic dogma in 1950 by Pope Pius XII.
Some interesting quotes from Wikipedia for follow-up study:¹
In Munificentissimus Deus (item 39) Pope Pius XII pointed to the Book of Genesis (3:15) as scriptural support for the dogma in terms of Mary’s victory over sin and death as also reflected in 1 Corinthians 15:54: “then shall come to pass the saying that is written, Death is swallowed up in victory”.
Although the Assumption (Latin: assumptio, “a taking”) was only relatively recently defined as infallible dogma by the Catholic Church, and in spite of a statement by Saint Epiphanius of Salamis in AD 377 that no one knew whether Mary had died or not, apocryphal accounts of the assumption of Mary into heaven have circulated since at least the 4th century.
On November 1, 1950, in the Apostolic Constitution Munificentissimus Deus Pope Pius XII declared the Assumption of Mary as a dogma:
By the authority of our Lord Jesus Christ, of the Blessed Apostles Peter and Paul, and by our own authority, we pronounce, declare, and define it to be a divinely revealed dogma: that the Immaculate Mother of God, the ever Virgin Mary, having completed the course of her earthly life, was assumed body and soul into heavenly glory.